Method of preparing cellulose pulp



Patented Jan. 13, 1931 UNITED STATES PATENT OFFICE ROBERT E. WOLF, OF NEW YORK, N. Y., AND RAYMOND P. HILL, 0]? GLEN ROCK, AND

RAYMOND S. HATCH, OF EAST ORANGE, NEW JERSEY METHOD OF PREPARING CELLULOSE PULP Nehru ring.

This invention relates to the preparation of cellulose pulp and particularly to an improved methodof treating wood and other ligno-cellul'ose material to separate and recover the constituents.

In the usual procedures for the recovery of cellulose, wood, .for exam le, is reduced to the form of chips which .are charged into a closed digester with a suitable liquor containing a chemical which will react with the ligneous portion of the wood. The digester is closed and the mass is heated directly or indirectly with steam or otherwise until the reaction is completed. The heating may continue for a period of from seven to thirty-six hours, more or less depending upon the character and con- 7 centration of the chemical,- the temperature compounds of the bases mentioned. The total sulphur dioxide content of such acid liquor will vary from one and one-half to six per cent approximately.

The acid liquor-containing sulphites, bi-' sulphites or both reacts with the ligneous portion of the wood to produce a complex lignin sulphonic acid compound which. may be partly or wholly combined with the bases present in the acid li'uor. compounds are highl v ionized, thatis, they belong to the class 0 so-called stron acids.

Cellulose is easily altered by acid ydrolysis in the presence of dilute strong acid at P elevated temperature. There is, consequently, a considerable loss of cellulose in the sulphite process which cannot be avoided under the normal conditions of operation. I

Moreover, the. lignin sulphonic acid compounds produced by the reaction are partly polymerized at the high temperature. The resulting resinous products are of little value in the arts. It is impracticable to separate The resulting- Application filed February a, 1929. -Serial No. 338,610.

like material to recover cellulose and other products without degradation or substantial oss.

Another object of the invention is to efiect a considerable saving in the amount of sulphur consumed per ton of cellulose produced.

The method depends'upon the application of anhydrous liquid sulphur dioxide or solutions thereof in non-aqueous solvents to the cellulose material. Sulphur dioxide is liquid at ordinary atmospheric temperature under a pressure of approximately 100 pounds per square inch. It can be prepared" and utllized, therefore, as a liquid at that' pressure. It is soluble in non-aqueous solvents such as glycerine, ethylalcohol, chlo- 7 rine componds oi acetylene and other organic solvents and can be utilized for the purpose of the invention in such solutions.

To effect the conversion of ligneous compounds in wood into lignin sulphonic acid a certain proportion of water is required. Water is, however, present in the wood in sufficient proportion to ensure the completion of the reaction. Extraneous water is not required, therefore, and 'as hereinbefore indicated it is detrimental inasmuch as the "presence of surplus water induces the degradation of the cellulose.

We have discovered that wood and similar cellulose material can be effectively treated with anhydrous liquid sulphur dioxide or non-aqueous solutions thereof to separate the cellulose therefrom. The cellulose is recovered in a substantially pure condition. The lignin sulphonic acid is substantially unpolymerized and can be separated readily t can be utilized for various purposes.

Furthermore the procedureavoids substantial losses of sulphur dioxide which are incident to the sulphite process as heretofore practised. The amount of'sulphur consumed 5 per ton of pulp recovered is, therefore, re-

duced-materially. a v

In carrying out the invention, we prefer to employ anhydrous liquid sulphur dioxide. The liquid can be prepared in the usual manner by'burning "sulphur, purifying the gas, andcom ressing it to the required pressure to efiect iquefaction at normal atmospheric temperature.

The wood or other material is prepared,

for example, in the form of chips and is charged into a digester of the usual form. Such digesters are capable of withstanding pressures in excess of those required for the method. Anhydrous liquid sulphur dioxide is introduced to the digester and the mixture is subjected to a pressure'of approximately one hundred and twenty-five pounds per square inch atordinary atmospheric or slightly elevated temperature, for example 5 60 to 100 F. The ressure and temperature P can be varied considerably, it being necessary merely to maintain the sulphur dioxide in liquid form.

The low surface tension of'the liquidsul- 3o phur dioxide facilitates the penetration of the wood. The pressure likewise aids the penetration. The sulphur dioxide in the presence of water contained in the wood readily reacts with the ligneous material, converting it into relatively simple lignin sulphonic acid compounds. When the reaction is complete, or after a period "varying from two to eight hours, the liquid sulphur dioxide is withdrawn under ressure to avoid 40 vaporizing it. The residue 0 sulphur dioxide is separated readily from the wood by the introduction of steam, air or an inert gas, and

the sulphur dioxide is recovered for further use after reliquefactiom.

The material iiitife digester, including the cellulose and the lignin sulphonic acid compounds, is then treated with water or a solution of the bases including alkali or alkaline earth metals to dissolve the lignin sulphonic acid compounds which may be recovered'by evaporation or otherwise. The cellulose remains undissolved and after suitable wash? ing to remove residual impurities it can be utilized for any of the purposes for which-it is adapted.

It will ployed in digesting the materia is very low as compared with temperatures employed in the sulphite process.- Hence there is no tendency to degrade the cellulose or to polymerize the lignin. compounds. Losses from these sources are avoided, and the yield of cellulose is correspondingly higher. There is likewise no loss of sulphur, in the form of inorganic be noted that the tern erature em- 4 sulphates or in gas which is dischargedfto the atmosphere, and the com licated recovery system which is usually use to recover sulphur dioxide in the sulphite continually under pressure, cannot escape and is easily stored and returned for further use.-

' Instead of using liquid sulphur dioxide we may employ non-aqueous solutions of sulphur dioxide in solvents such as glycerine, alcohol, etc. The method is substantially the same. The chips are subjected in the digester to the solution at approximately the temperature and pressure hereinbefore mentioned. The reaction is effected in the presence, of water which is in the wood so that .no extraneous rocess is not required. The liquid sulphur ioxide, being water is introduced. When the reaction is completed the solution of sulphur dioxide is withdrawn and the wood is then washed with water or'alkaline'solutions to separate the lignin sulphonic acid leaving the cellulose which, afterfinal washing, can be used as de prises converting the ligneous portion thereof into soluble compounds by subjecting ligno-cellulose material to the action of a nonaqueous liquid containing sulphur dioxide.

2. The method of preparingzcellulose pulp from ligno-cellulos'e material which comprises converting the ligneousportion thereof into soluble compounds bysubjecting ligno-cellulose material to the action of a non-aqueous liquid containing sulphur .dioxide, withdrawing the liquid and washing the converted ligneous material from the cellulose.

3. ,The method of preparing cellulose pulp from ligno-cellulose material which comprises converting the ligneous ortion thereof intosoluble compounds y subjecting ligno-cellulose material to the action of a non-aqueous liquid containing sulphur di-' oxide at approximately ordinary atmospheric temperature.

prises converting the ligneous portion thereof into soluble compounds by subjecting ligno-cellulose materialto the action of a non-aqueous liquid containing sulphur di- 4. The method of preparing cellulose pulp' from ligno-cellulose .material which com-- 5. The method of preparing cellulose pulp from ligno-cellulose material which comprises converting the ligneous ortion thereof into soluble compounds y subjecting ligno-cellulose materlal to the actlon of anhydrous li uid sulphur dioxide.

6. The met od of preparing cellulose pulp from ligno-cellulose material which comprises converting the ligneous ortion thereof into soluble compounds y subjecting ligno-cellulose material to the action of anhydrous liquid sul hur dioxide, withdrawing the liquid an 'washing the converted ligneous material from the cellulose.

' 7. The method of preparing cellulose pulp from ligno-cellulose material which comprises converting the ligneous ortion thereof into soluble compounds ligno-cellulose material to the action of anhydrous liquid sulphur dioxide, withdrawing the liquid, removin the residual sulphur dioxide and washing the converted igneous material from the cellulose.

8. The method of preparing cellulose pulp from ligno-cellulose material which comprises converting the ligneous ortion thereof into soluble compounds y subjecting ligno-cellulose material to the action of anhydrous liquid sulphur dioxide at substantially ordina atmospheric temperature.

9. The'met 0d of preparing cellulose pulp from ligno-cellulose material which comprises converting the lig'neous ortion thereof into soluble compounds y subjecting ligno-cellulose material to the action of anhydrous liquid sulphur dioxide at substantially ordlnary atmospheric temperature, withdrawing the liquid, and washing the con verted ligneous material from the cellulose.

10. The method of-prepari cellulose pulp from ligno-ce-llulose materifi which comprises converting the ligneous ortion thereof into soluble compounds y subjecting ligno-cellulose material to the action of anhydrous liquid sulphur dioxide at substantially 'tdinary atmospheric temperature, withdra. ing the liquid under pressure suflicient to prevent evaporation thereof, and washing the converted ligneous material from the cellulose.

. .In testimony whereof we afiix our signatures.

ROBERT B. WOLF. RAYMOND P. HILL. RAYMOND S. HATCH.

y subjecting 

